Field of the Invention
The present invention relates generally to lighting fixtures, and in particular to high bay lighting fixtures with one or more enhanced thermal dissipation features.
Description of the Related Art
Industrial or commercial buildings are often illuminated by free-standing lighting fixtures that may be suspended from the ceiling. Certain types of commercial or industrial environments, such as store aisles or warehouses, require lighting that is designed to provide a high degree of luminosity, while still maintaining control over glare. The type of lighting fixture that satisfies these requirements is commonly referred to as bay lighting.
Bay lighting may be classified as high bay or low bay, depending on the height of the lighting fixture, which is usually the distance between the floor of the room seeking to be illuminated and the fixture itself. Naturally, large industrial or commercial buildings with overhead lighting are typically illuminated with high bay lighting fixtures.
In order to sufficiently illuminate this type of environment, a high bay lighting fixture with a high intensity discharge can be used. Yet high intensity lighting fixtures often use light sources such as incandescent, halogen, or fluorescent bulbs, which can have short life spans, difficulty maintaining their intensity, and/or high maintenance costs. The advent of solid state lighting devices with longer life spans and lower power consumption presented a partial solution to these problems.
One example of a solid state lighting device is a light emitting diode (LED). LEDs convert electric energy to light, and generally comprise one or more active layers of semiconductor material sandwiched between oppositely doped layers. When a bias is applied across the doped layers, holes and electrons are injected into the active layer where they recombine to generate light. Light is emitted from the active layer and from all surfaces of the LED.
In comparison to other light sources, LEDs can have a significantly longer operational lifetime. Incandescent light bulbs have relatively short lifetimes, with some having a lifetime in the range of about 750-1000 hours. Fluorescent bulbs can also have lifetimes longer than incandescent bulbs such as in the range of approximately 10,000 to 20,000 hours, but provide less desirable color reproduction. In comparison, LEDs can have lifetimes between 50,000 and 70,000 hours. The increased efficiency and extended lifetime of LEDs is attractive to many lighting suppliers and has resulted in LED lights being used in place of conventional lighting in many different applications. It is predicted that further improvements will result in their general acceptance in more and more lighting applications. An increase in the adoption of LEDs in place of incandescent or fluorescent lighting would result in increased lighting efficiency and significant energy saving.
As mentioned above, high bay lighting fixtures usually require a high intensity light source, based on the illumination requirement of their industrial or commercial environment. Yet a problem with most high intensity lighting devices is that they can draw large currents, which in turn generates significant amounts of heat. High intensity LEDs are no exception. The type of high intensity LEDs used in high bay lighting fixtures likewise produce a large amount of heat. Even if an LED is particularly efficient, the amount of heat that it produces can still be substantial. Without an effective way to dissipate heat that is produced, LED light sources can suffer elevated operating temperatures, which can increase their likelihood of failure. Therefore, in order to operate most effectively and reliably, LED light sources need an efficient method to dissipate heat.
One common method that LED high bay lighting fixtures use for heat dissipation is a heat sink. A heat sink is essentially an element that is in thermal contact with a light source, so that it dissipates heat from the light source. Whenever the heat dissipation ability of the basic lighting device is insufficient to control its temperature, a heat sink is desirable. Some common heat sink materials are aluminum alloys, but other materials or combinations of materials with good thermal conductivity and heat dissipation potential will suffice.
Many common LED high bay lighting fixtures include a heat sink that is in thermal contact with the light source. FIG. 1 displays one such example of a typical LED high bay lighting fixture 10. Included in this example are an LED driver housing 12, a heat sink 14, and a spun housing 16. The heat sink 14 can be a large “extrusion/stack fin” heat sink, which can be made of a heat conductive material such as aluminum. Likewise, the spun housing 16 can also be composed of a metal such as aluminum. The large size of the heat sink 14 is typical in order to dissipate the heat from a high intensity light source commonly used in high bay lighting.
FIG. 2 displays another example of a traditional LED high bay lighting fixture 20. In this example, the high bay lighting fixture 20 includes a high intensity discharge ballast 22 and a spun housing 26. Lighting ballasts can refer to any component that is intended to limit current flow through a light source. The ballast 22 displayed in FIG. 2 is a common choice for many high bay lighting fixtures and other high intensity discharge lighting fixtures. As in the previous example, the spun housing 26 is typically made of aluminum.
Typically and as shown in FIGS. 1 and 2, driver electronics are installed directly above an emitter array, meaning that the electronics and emitters share a primary heat dissipation path. Heat from the emitters will rise, often through a heat sink, to the location of the driver electronics. Because the driver electronics are also one of the main heat sources in such a fixture, heat may not dissipate as effectively from the emitters as if there were a thermal dissipation path free of other heat sources.
FIGS. 3A and 3B are a side view and a side thermal imaging of a prior art LED high bay lighting fixture 30 including a housing 36 and a driver housing 32. As can be seen in FIG. 3B, the LED driver housing 32 is a heat source. In a typical prior art fixture, driver electronics can contribute about 10% of the total heat generated by the fixture during operation, although in some fixtures this percentage can be lower or higher. The heat generated by the driver can cause the emitter operating temperature to rise, leading to a loss in intensity and/or efficiency. This fixture is similar in many respects to the LED fixture 10 from FIG. 1. However, in this embodiment the LED driver housing 32 is about three to six feet directly above the light emitting elements (not shown). This connection can be made using a steel pipe 34, which can also provide electrical connection. While the light emitting elements are the main source of heat within the fixture, the driver electronics also contribute a significant amount to the overall heat generation of the fixture. Separating the light engine from the driver housing 32 in this manner can improve thermal dissipation to a certain extent, but also increases the overall height of the fixture, which may be undesirable.